Any idea? Fossil find Bay Area, California

[RCD]

Found these along a creek bed about 30 miles inland at about 500 ft. elevation. Any ideas? 

 

[Lone Hunter]

They look like Rugose coral to me,  the first picture appears to be one with the tentacles extended which if it is it's the first one I've seen like that.  Of course I could be way off. 

[DPS Ammonite]

Give us a better locality especially for those that might not know what Bay you are referring to. If you are referring to the San Francisco Bay Area, rugose corals are unlikely since there are no Paleozoic rocks nearby. Solitary non-rugose corals probably occur in the Jurassic and later rocks.

[FranzBernhard]

17 minutes ago, Lone Hunter said:

They look like Rugose coral to me

Yes!

 

17 minutes ago, Lone Hunter said:

the first picture appears to be one with the tentacles extended which if it is it's the first one I've seen like that.

Yes, nice faker! Just a matter of direction of sectioning the specimen. We are seeing the septa, pretending to be, well... 

[FranzBernhard]

1 minute ago, DPS Ammonite said:

rugose corals are unlikely since there are no Paleozoic rocks nearby.

Any chance of being just a clast in those conglos, breccias and melanges?

 

@RCD, is it a one of a kind find?

Franz Bernhard

[DPS Ammonite]

Here is an example of a solitary Jurassic coral that sort of looks like a Paleozoic rugose coral. Never heard of any naturally occurring Paleozoic fossils in the San Francisco Bay Area.

 

https://woostergeologists.scotblogs.wooster.edu/2015/04/03/woosters-fossil-of-the-week-a-disturbingly-familiar-coral-from-the-middle-jurassic-of-southern-israel/

 

[RCD]

Thanks so much all for the thoughtful replies. Yes I am in the San Francisco Bay Area, although the observation is about 25 miles inland/east of the bay shoreline, so I am not sure it is technically considered "Bay Area", rather in the transition zone between the SF Bay Area and the Central Valley. The location is at the bottom of a very deep seasonal creek channel about 500 ft. elevation. I stumbled across the area which is quite remote and I don't think well known. A few miles away from the location is a well known late Miocene formation. I found a bunch of interesting fossils at this new spot, and both the base rock and fossils themselves seemed of a different character than the well-known "shell" spots here in the East Bay nearby. The creek has cut deep into some interesting layers with many large sedimentary boulders and bedrock, I'd say the mix is about 40% sedimentary, 40% metamorphic and 20% igneous. 

[FranzBernhard]

3 hours ago, RCD said:

I found a bunch of interesting fossils at this new spot,

Would you like to show off some more ? Thanks!

 

I can not comment on the geology, just know, that your area is at least as complex as the Alps....

 

Franz Bernhard

[DPS Ammonite]

Look at this map to see if you can give us an idea of what age, type  or formation the rock is:

 

https://pubs.usgs.gov/sim/2006/2918/sim2918_geolposter-hires.pdf

 

Was there a layer of similar rocks or was this a boulder that was reworked and emplaced in a newer conglomerate? Can you show us other fossils in a similar rock to help us date them? If I see typical Paleozoic fossils such as crinoids, brachiopods and trilobites then maybe an isolated clast somehow survived subduction trench warfare relatively unmetamorphosed.

Edited May 14, 2022 by DPS Ammonite

[MikeR]

Most of my fossil collecting trips to the SF area, I found mainly Miocene marine fossils.  I would go with single polyp scleractinian corals.

 

Mike

Edited May 14, 2022 by MikeR

[RCD]

12 hours ago, DPS Ammonite said:

Look at this map to see if you can give us an idea of what age, type  or formation the rock is:

 

https://pubs.usgs.gov/sim/2006/2918/sim2918_geolposter-hires.pdf

 

Was there a layer of similar rocks or was this a boulder that was reworked and emplaced in a newer conglomerate? Can you show us other fossils in a similar rock to help us date them? If I see typical Paleozoic fossils such as crinoids, brachiopods and trilobites then maybe an isolated clast somehow survived subduction trench warfare relatively unmetamorphosed.

Oh my gosh, that map is AMAZING!!! Huge thanks for sharing. I carefully examined and the location looks to be mainly the Great Valley complex sedimentary rocks (Cretaceous), but also bordering Eocene sedimentary, Miocene sedimentary, and possibly the bedrock in the deep cut creek bottom of Pleistocene alluvium, so it is a quite diverse spot, which explains the impressive range of rock types I was seeing. Again, huge thanks, what an awesome map and the thoughtful comments. Stoked to be on this forum.